Quilting is a special art in the general field of sewing in which patterns are stitched through a plurality of layers of material over a two dimensional area of the material. The multiple layers of material normally include at least three layers, one a woven primary or facing sheet that will have a decorative finished quality, one a usually woven backing sheet that may or may not be of a finished quality, and one or more internal layers of thick filler material, usually of randomly oriented fibers. The stitched patterns maintain the physical relationship of the layers of material to each other as well as provide ornamental qualities.
Frequently, it is desirable to combine stitched patterns with printed patterns in mattress cover and other quilt manufacture. Application of the quilted pattern requires the application of ink to fabric, which, unlike paper, plastic or other smooth surfaces, presents a texture, or third dimension or depth, to the surface on which the printing is applied. A highly preferred method of applying ink to fabric is by jetting the ink onto the fabric by the process known as ink jet printing.
In ink jet printing, two categories of inks are used, solvent based inks and UV curable inks. Solvent based inks include either water or organic based solvents. Solvent based inks are cured by evaporation of the solvents. Some solvent based inks cure only by air drying, but many require the application of heat to enhance the evaporation of the solvent and, in some cases, to facilitate a chemical change or polymerization of the ink. UV curable inks include monomers that polymerize when exposed to UV light at a threshold energy level.
Heat or air curable inks that are organic solvent based or water based inks usually do not have the high color intensity that UV curable inks might have because the pigments or dyes that produce the color are somewhat diluted by the solvent. Furthermore, organic solvents can produce an occupational hazard, requiring that costly measures be taken to minimize contact of the evaporating solvents by workers and to minimize other risks such as the risks of fire. Solvent based inks also tend to dry out and eventually clog ink jet nozzles.
UV curable inks are capable of providing higher color intensity and do not present the hazards that many solvent based inks present. Printing with UV curable ink on fabric, however, presents other problems that have not been solved in the prior art. To cure UV ink, it must be possible to precisely focus a UV curing light onto the ink. UV ink, when jetted onto fabric, particularly onto highly textured fabric, is distributed at various depths over the texture of the fabric surface. Furthermore, the ink tends to soak into or wick into the fabric. As a result, the ink is present at various depths on the fabric, so that some of the ink at depths above or below the focal plane of the UV curing light evade the light needed to cause a total cure of the ink. In order to cure, UV ink must be exposed to UV light at an energy level above a curing threshold. However, increasing the intensity of the curing light beyond certain levels in order to enhance cure of the ink can have destructive effects on the fabric.
UV curing of jetted ink on fabric has a limited cure depth that is determined by the depth of field of the focused curing UV light. Therefore, the UV light proceeds to cure only about 90%, or 97%, and can be even up to about 99% of the ink when deposited on fabric. However, if more than an order of magnitude of approximately 100 parts per million (PPM) (0.01%) of the total volume of the jetted ink remains uncured, persons sensitive to the uncured monomers can suffer reactions. This is particularly unacceptable for fabrics such as mattress covers, as well as for clothing and many other fabrics.
Further, ink jet printing can be carried out with different ink color dots applied in a side-by-side pattern or in a dot-on-dot (or drop-on-drop) pattern. The dot-on-dot method is capable of producing a higher color density, but the higher density dot-on-dot pattern is even more difficult to cure when the cure is by UV light.
In addition, UV ink can be applied quickly to reduce wicking and UV ink can be developed to allow minimized wicking. Some wicking, however, helps to remove artifacts. Further, inks developed to eliminate wicking leave a stiff paintlike layer on the surface of the fabric, giving the fabric a stiff feel or "bad hand". Therefore, to reduce the UV curing problem by eliminating wicking is not desirable.
For the reasons stated above, UV curable inks have not been successfully used to print onto fabric. Heat curable inks can be cured on fabric. As a result, the ink jet printing of solvent based inks and heat curable or air dryable ink has been the primary process used to print on fabric. Accordingly, the advantages of UV curable ink jet printing have not been available for printing onto fabric.
There exists a need in printing of patterns onto mattress ticking and mattress cover quilts, as well as onto other types of fabrics, for a process to bring about an effective cure of UV curable inks and to render practical the printing with UV curable inks onto fabric.